I had a '73 Dart Swinger slant six that would die sporadically and refuse to restart for a time, then run well for weeks before the problem recurred. No spark. When I finally got around to keeping some test tools in the car, I found that the test light ground to coil negative test (should flash when cranked) was staying off. So no spark because the coil wasn't getting switched; the ignition module was switched 'on' full time and the ballast resistor was extremely hot.
Turned out to be the ignition module, but I'd already replaced the ballast resistor, reluctor, and pickup and confirmed the state of the wiring and power.
The car ran very well for the remaining years I had it.